1. Field of the Invention
This invention relates to a method and apparatus for determining the flatness or planarity of a surface and, specifically, to a method and apparatus for determining the flatness or planarity of a surface using a computerized optics technique.
2. Description of Related Art
The flatness of industrial films (such as, Mylar.RTM. polyester films) is of critical importance to processes involved in film preparation for its eventual application. For example, a non-flat film will cause processing problems in the manufacture of floppy discs. The flatness or planarity of films for this application has been traditionally determined by a subjective, visual inspection of the product. As a result of its subjective nature, this process suffers from inaccuracy and inconsistency. It further lacks adequate sensitivity to differentiate among various levels of flatness.
Various attempts have been made to determine surface flatness or presence of imperfections in the surface of an object. For example, U.S. Pat. No. 4,629,319 discloses a method and apparatus for detection and quantification of defects such as dents, creases, low spots, flat spots, etc., in surfaces, such as automobile body panels, refrigerator panels, furniture panels, and aircraft panels. U.S. Pat. No. 4,627,733 discloses a device for optically measuring the flatness of a slider head surface of a magnetic tape recording apparatus. U.S. Pat. No. 4,468,120 discloses an apparatus for detecting the presence of a foreign substance adhering to a surface. In U.S. Pat. No. 3,885,875, an electroptical device (i.e., a laser beam) provides an output proportional to a surface profile. U.S. Pat. No. 3,439,988 discloses illuminating a surface with a pattern of lines and visually inspecting the reflected surface appearing on a target.
Additionally, on page 92 of the February, 1988 issue of Plastics World there is described a surface analyzer available from Ashland Chemical Co., of Columbus Ohio, which utilizes a dot laser beam path reflected from a surface onto a screen, with video camera recorded images of the waviness of the path being digitized and analyzed by a minicomputer. Further, U.S. Pat. No. 4,853,777 assigned to Ashland Chemical Co. recently issued describing a surface analyzer which may be the analyzer described in the February, 1988 issue of Plastics World.
It is an object of this invention to provide a method and apparatus for determining the flatness or planarity of a surface which is accurate, quantitative and reproducible.
It is another object of this invention to provide a method and apparatus for determining the flatness or planarity of a plurality of lanes or zones on a surface which is accurate, quantitative and reproducible.
It is a further object of this invention to provide a method and apparatus for determining the flatness or planarity of a surface which is accurate, quantitative and reproducible using a computerized optics technique.